The present invention pertains to metal cutting torch control systems and, more particularly, to an apparatus and method for detecting the edge of a workpiece being cut with a cutting torch whereby unintended contact of the torch with the workpiece is obviated.
On thermal cutting machines, utilizing non-contact cutting torches, means are typically provided for maintaining the height of the cutting torch above the workpiece, typically a generally flat metal plate. However, because the plate may be warped and not sit flat and level with respect to the overhead cutting tool operating in a horizontal X-Y plane, height adjustment is necessary to prevent damaging contact between the torch or torches and the plate. This need is even more critical when the tools are positioned to provide bevel cutting on the plate.
Mechanical torch height sensing and control systems are known. One such system utilizes a vertically free floating probe that rides on the surface of the plate and whose vertical movement is monitored and used to adjust the height of the cutting torch above the plate in response to plate surface irregularities in order to maintain the desired height of the cutting torch above the plate. In such systems, one or more torches are mounted on a support attached to a motorized servo controlled vertical slide. The plate contact probe is mounted on the same support and positioned as close as possible to the torch or torches without being subject to damage or destruction by the heat of the cutting process. As the probe rests on and slides over the surface of the plate, the vertical position of the probe is measured by a linear transducer and the position information is processed by a CNC/PLC which provides a signal to move the torch slide up or down. By permitting the probe and torch to operate independently of each other, different torch-to-plate gaps may be set for different cutting conditions and workpiece materials. In one prior art method of the control, the plate rider probe assembly is mechanically adjusted up or down in relation to the cutting torch. The control then adjusts the height of the torches so that the voltage across the linear transducer maintains a constant value. In another prior art method, the transducer voltage value is programmed, thereby changing the operating height between the torch and the plate or other workpiece surface.
During normal cutting, without the system of the present invention, the torch may move in a path that closely approaches the edge of a cutout portion or the edge of the plate. In either situation, the height sensing probe will move off and out of contact with the plate and move downwardly. The height sensing system will respond by directing the torch to follow vertically downwardly, resulting in the torch crashing into the plate on which it is cutting.